Spontaneous solid electrolyte interface formation in uncycled sodium half-cell batteries: using X-ray photoelectron spectroscopy to explore the pre-passivation of sodium metal by fluoroethylene carbonate before potentials are applied

Abstract

Testing sodium battery technology relies on a half-cell setup with sodium metal as the counter electrode. Herein, we show that sodium metal reacts with conventional carbonate electrolyte to form the solid electrolyte interface (SEI) on the working electrode spontaneously in a half-cell, without applying any external potential. Fluoroethylene carbonate prevents this spontaneous SEI formation by pre-passivating sodium metal, again before any potentials are applied or current is passed.